Particulate filters for engine exhaust are gaining importance as engine manufacturers seek to reduce emissions. Particulate filters are used to filter out particulate matter from the engine's exhaust stream, and to periodically regenerate when the filter reaches a certain degree of clogging. Regeneration of the filter is typically accomplished by increasing the temperature of the particulate filter to a point where the accumulated particulates are burned off, thereby unclogging the filter.
Catalysts of various compositions are frequently used to elevate the temperature of the particulate filter. Catalysts, however, typically only function well when they are above their respective “light off” temperature. The “light off” temperature for a catalyst is typically a temperature above which the catalyst is able to convert unburned hydrocarbons at some predetermined efficiency. Typically at temperatures below the “light off” temperature the catalyst converts a negligible amount of hydrocarbons, while at temperatures above the “light off” temperature, the catalyst may operate at a substantially higher efficiency.
The unburned hydrocarbons may be delivered to the catalyst through a variety of ways, such as, for example, injecting a shot of diesel fuel after substantial combustion within a cylinder has occurred. The diesel fuel then exits the cylinder through the exhaust valve and reaches the catalyst in relatively unchanged form.
Control of the temperatures of the catalyst and particulate filter have been relatively crude, and a better techniques and devices for performing this function are desired.